Tuned magnetism for quantum components

Columbia University chemists and physicists recently found a link between tunable electronic magnetic properties in a 2D semiconductor that could potentially be applied to quantum computing, spintronics, and other fundamental research.

Created in the lab of chemist Xavier Roy, chromium-sulfide-bromide (CrSBr) is chemistry that is called a van der Waals crystal, which can be peeled into stackable, 2D layers that are just a few atoms thin.

It is due to the unique nature of van der Waals heterostructures – basically a custom-tailored atomic structure that consists of stacks of two-dimensional materials in a precisely controlled order – that allows researchers to tune magnetism to its desired effect.

You can read more about spintronics and van der Waals crystals at Graphene opens door to 'spintronic' tech in the June 10, 2020, edition of Metal Tech News.

Unlike related materials that are quickly destroyed by oxygen and water, CrSBr crystals are stable at ambient conditions and can maintain their magnetic properties at a relatively high temperature of minus 280 degrees Fahrenheit – superconductors still require incredibly low temps to work property – while also avoiding the need for expensive liquid helium cooling to temperatures as low as -450F.

"CrSBr is infinitely easier to work with than other 2D magnets, which lets us fabricate novel devices and test their properties," said Evan Telford, a postdoctoral researcher in the Roy lab.

Last year, a University of Washington and Columbia University collaboration found a link between magnetism and how CrSBr responds to light. In the current work, Telford led the effort to explore its electronic properties.

Using an electric field to study CrSBr layers across different electron densities, magnetic fields, and temperatures – parameters that can be adjusted to produce different effects in a material – as electronic properties in the crystals changed, so too did its magnetism.

"Semiconductors have tunable electronic properties," said Roy. "Magnets have tunable spin configurations. In CrSBr, these two knobs are combined. That makes CrSBr attractive for both fundamental and research, and for potential spintronics application."

Spintronics is a relatively new approach to developing electronics, where both memory devices (RAM) and logic devices (transistors) utilize rotation, or spin – an intrinsic property of electrons that allows them to behave like tiny magnets themselves and generate an electrical charge.

Information in computers is transmitted through semiconductors by the movement of electrons and stored in the direction of the electron rotation in magnetic materials. To shrink devices while improving their performance is the goal in the emerging field of spin-electronics.

Ultimately, spintronics is a combination of modern electrical components and magnetism, at a nanoscale, that could lead to the next generation of high-speed electronics, and we already see that today, in solid-state hard drives.

Yet the difficulty lies in magnetism itself; it's tricky to measure directly, especially as the size of the material shrinks, explained Telford, but it's easy to measure how electrons move with a fundamental electrical system called resistance.

In CrSBr, resistance can serve as a proxy for otherwise unobservable magnetic states.

"That's very powerful," added Roy, especially as researchers look to one day build microchips out of such 2D magnets, which could be used for quantum computing and to store inestimable amounts of data in even smaller spaces.

"Unsurprisingly, the link between the material's electronic and magnetic properties was due to defects in the layers, which for the team was a lucky break," said Telford. "People usually want the 'cleanest' material possible. Our crystals had defects, but without those, we wouldn't have observed this coupling."

From there, the Roy lab has continued to experiment with ways to grow more peelable van der Waals crystals with deliberate defects, to improve the ability to fine-tune the material's properties. The team is also exploring whether different combinations of elements could function at higher temperatures while still retaining those valuable combined properties.